1. Field of the Invention
The present invention generally relates to a channel allocation technique, and more particularly, to channel allocation for an access point in a mesh network (an adhoc network or a self-organizing network) structured by multiple access points with wireless communication abilities.
2. Description of the Related Art
A wide range of applications of mesh networking is being proposed. For example, an application to a home network in which consumer electronics, such as a television set or a DVD player, are provided with functions of access points is proposed. In such a network, audio and video data are transmitted from the DVD player to the television set, in response to a request from the television set, without using cable connections or other wired connections. To push such an application to practical use, the data transmission rate between access points has to be increased.
FIG. 1 is a schematic diagram of a conventional mesh network, in which the number of channels allocated is the same as that of the radio radio interfaces of the access point. Each of the access points AP1-AP4 has two radio radio interfaces, which radio interfaces are set to channels f1 and f2, respectively. The number of channels is not limited to this example, and channels to be allocated may be increased in accordance with the number of radio radio interfaces if many radio radio interfaces are used.
By allocating multiple channels to each access point, simultaneous communication with other access points using different channels is realized, and the transmission rate between access points is increased. In this example, since the number of radio radio interfaces is equal to that of the channels, it is unnecessary to allocate a different set of channels to each access point separately.
FIG. 2 is a schematic diagram of a conventional mesh network, in which the number of channels available in the network is more than that of the radio radio interfaces of each access point. By increasing the number of channels, the efficiency of the mesh network is temporarily improved. However, because all the channels cannot be used simultaneously at the radio radio interfaces of each access point, the access points are clustered. For example, in FIG. 2, access points AP1 and AP4 are grouped in a cluster that uses a channel set of channels f1 and f3, while access points AP3 and AP2 are grouped in a cluster that uses a channel set of channels f1 and f2. In this context, a cluster is a logical group of nodes that use the same channel set.
In this case, two channels can be used simultaneously between access points AP1 and AP4 grouped in the same cluster. Similarly, two channels are used simultaneously between access points AP3 and AP2 in the same cluster. Accordingly, high-rate transmission can be performed. For the data transmission between access points belonging to different clusters is used the common channel of frequency f1, and accordingly, the transmission rate is decreased.
FIG. 3 is an example of conventional access point clustering based on network topology, which method is designed so as to group those access points located close to each other together in the same cluster in the mesh network. Access points AP1-AP3 are grouped in the first cluster, access points AP4-AP7 are put in the second cluster, and access points AP8-AP10 are arranged in the third cluster. The criterion and the control sequence as to which range of access points are grouped in the same cluster are different among proposals. See, for example,
(1) Mizuno, et al. “An Evaluation of Self-organization Method for Multihop Wireless Networks”, IEICE, Technical Report, Vol. 102 No. 281 ISSN 0913-5685 RCS 2000-137 (2002-08); and
(2) Jing Zhu, et al., “Maximizing Aggregate Throughput in 802.11 Mesh Networks with Physical Carrier Sensing and Two-Radio Multi-Channel Clustering”, in Proceedings of NSF-FPI Workshop on Pervasive Computing and Networking, Apr. 29-30, 2004.
The above-described channel allocation (clustering) based on the physical position of the nodes is advantageous in that the control operation is easy.
In the conventional method, channel allocation to the access points in the mesh network is carried out based on the physical position of the nodes, and high-speed communication can be performed between access points in the same cluster because of the sufficient number of available channels. In contrast, communication between access points across clusters cannot be carried out at high rate because fewer channels are available for inter-cluster communication.
In a mesh network, communication conditions are unfixed, always changing depending on situations, and accordingly, a large amount of transmission may often occur across clusters. In such a case, the throughput falls down, and the network efficiency is degraded.